How to use the broccoli-funnel.prototype function in broccoli-funnel

// An array and FSTree, respectively, representing the dependency graph of the
  // entry point or the non-dependency graph.
  this._depGraph = undefined;
  this._depGraphTree = undefined;
  this._nonDepGraph = undefined;
  this._nonDepGraphTree = undefined;

  Plugin.call(this, [inputNodes], {
    annotation: options.annotation,
    persistentOutput: true
  });
  this.options = options;
}

RollupFunnel.prototype._copy = Funnel.prototype._copy;

/**
 * Constructs an FSTree from the passed in paths.
 *
 * @param {Array} paths
 * @return {FSTree}
 */
RollupFunnel.prototype._getFSTree = function(paths) {
  var inputPath = this.inputPaths[0];
  var entries = paths.map(function(entryPath) {
    var absolutePath = path.join(inputPath, entryPath);
    var stat = existsStat(absolutePath);

    if (!stat) {
      return;
    }